Real-time quantitative reverse transcription-polymerase chain reaction to detect propionibacterial ribosomal RNA in the lymph nodes of Chinese patients with sarcoidosis

The aim of this study was to investigate the diagnostic value of using the copy number of propionibacterial rRNA as a biomarker for sarcoidosis. Ribosomal RNA of Propionibacterium acnes and P. granulosum was measured by real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) using formalin-fixed and paraffin-embedded tissue of lymph node biopsy from 65 Chinese patients with sarcoidosis, 45 with tuberculosis and 50 controls with other diseases (23 with non-specific lymphadenitis and 27 with mediastinal lymph node metastasis from lung cancer). The receiver operating characteristic (ROC) curve was analysed to determine an optimal cut-off value for diagnosis, and the diagnostic accuracy of the cut-off value was evaluated in additional tissue samples [24 patients with sarcoidosis and 22 with tuberculosis (TB)]. P. acnes or P. granulosum rRNA was detected in 48 of the 65 sarcoidosis samples but only in four of the 45 TB samples and three of the 50 control samples. Analysis of the ROC curve revealed that an optimal cut-off value of the copy number of propionibacterial rRNA for diagnosis of sarcoidosis was 505 copies/ml with a sensitivity and specificity of 738 and 926%, respectively. Based on the cut-off value, 19 of the 24 additional sarcoidosis samples exhibited positive P. acnes or P. granulosum, whereas only one of the 22 additional TB samples was positive, resulting in a sensitivity and specificity of 792 and 955%, respectively. These findings suggest that propionibacteria might be associated with sarcoidosis granulomatous inflammation. Detection of propionibacterial rRNA by RT-PCR might possibly distinguish sarcoidosis from TB.